1. Field of the Invention
This invention relates to a vulcanization accelerator for chloroprene rubber capable of providing chloroprene rubber products possessed of improved physical properties. More particularly, it relates to a vulcanization accelerator for chloroprene rubber capable of providing chloroprene rubber products improved in physical properties, particularly tear strength and resistance to deterioration, and to a powdery vulcanization accelerator for chloroprene rubber which curbs the emission of odor during the manufacture of rubber products and permits easy handling.
2. Description of the Prior Art
Heretofore, ethylene thiourea (ETU) has been generally used as the vulcanization accelerator for choloroprene rubber. It is toxic and is suspected to be carcinogenic. Thus, appearance of some rubber vulcanization accelerator capable of providing chloroprene rubber products equivalent or superior to those provided by ETU has been in demand.
It has been disclosed that thioglycolic acid is useful as a polymerization regulator or rubber modifier for chloroprene (Japanese Publications of Unexamined Patent Applications Nos. 52556/1978 and 50285/1978). These techniques invariably aim to produce liquid polymers incorporating a terminal carboxyl group by homopolymerizing a chloroprene monomer or copolymerizing a chloroprene monomer with another monomer copolymerizable therewith in the presence of a mercapto-carboxylic acid. These techniques do not contemplate mixing mercapto-carboxylic acid as a vulcanization accelerator to chloroprene rubber immediately before the vulcanization thereof.
To the best of the inventor's knowledge, no one has ever tried incorporation of a thioglycolic acid ester in chloroprene rubber. Presumably the fact that thioglycolic acid esters are liquid and emit the odor peculiar to mercaptane has discouraged all attempts to adopt the esters for use in chloroprene rubber.